Acid criticism (7)
I believe the answer is:
vitriol
I believe this clue is a double definition.
'acid' is the first definition.
(I know that vitriol is a type of acid)
'criticism' is the second definition.
(I have seen 'Caustic criticism' mean 'vitriol' so perhaps 'criticism' could also mean 'vitriol')
(Other definitions for vitriol that I've seen before include "Caustic words" , "Scathing criticism - sulphuric acid" , "Sulphuric acid; malicious criticism" , "Sulphuric acid and hateful criticism" , "hostile criticism" .)